Enhanced Cycling Stability of Rechargeable Li–O2 Batteries Using High‐Concentration Electrolytes

The stability of electrolytes against highly reactive, reduced oxygen species is crucial for the development of rechargeable Li–O₂ batteries. In this work, the effect of lithium salt concentration in 1,2‐dimethoxyethane (DME)‐based electrolytes on the cycling stability of Li–O₂ batteries is investigated systematically. Cells with highly concentrated electrolyte demonstrate greatly enhanced cycling stability under both full discharge/charge (2.0–4.5 V vs Li/Li⁺) and the capacity‐limited (at 1000 mAh g^?1) conditions. These cells also exhibit much less reaction residue on the charged air‐electrode surface and much less corrosion of the Li‐metal anode. Density functional theory calculations are used to calculate molecular orbital energies of the electrolyte components and Gibbs activation energy barriers for the superoxide radical anion in the DME solvent and Li⁺–(DME) _n solvates. In a highly concentrated electrolyte, all DME molecules are coordinated with salt cations, and the C–H bond scission of the DME molecule becomes more difficult. Therefore, the decomposition of the highly concentrated electrolyte can be mitigated, and both air cathodes and Li‐metal anodes exhibit much better reversibility, resulting in improved cyclability of Li–O₂ batteries.     

Self‐Standing Porous LiCoO2 Nanosheet Arrays as 3D Cathodes for Flexible Li‐Ion Batteries

Self‐standing electrodes are the key to realize flexible Li‐ion batteries. However, fabrication of self‐standing cathodes is still a major challenge. In this work, porous LiCoO₂ nanosheet arrays are grown on Au‐coated stainless steel (Au/SS) substrates via a facile “hydrothermal lithiation” method using Co₃O₄ nanosheet arrays as the template followed by quick annealing in air. The binder‐free and self‐standing LiCoO₂ nanosheet arrays represent the 3D cathode and exhibit superior rate capability and cycling stability. In specific, the LiCoO₂ nanosheet array electrode can deliver a high reversible capacity of 104.6 mA h g^?1 at 10 C rate and achieve a capacity retention of 81.8% at 0.1 C rate after 1000 cycles. By coupling with Li₄Ti₅O₁₂ nanosheet arrays as anode, an all‐nanosheet array based LiCoO₂//Li₄Ti₅O₁₂ flexible Li‐ion battery is constructed. Benefiting from the 3D nanoarchitectures for both cathode and anode, the flexible LiCoO₂//Li₄Ti₅O₁₂ battery can deliver large specific reversible capacities of 130.7 mA h g^?1 at 0.1 C rate and 85.3 mA h g^?1 at 10 C rate (based on the weight of cathode material). The full cell device also exhibits good cycling stability with 80.5% capacity retention after 1000 cycles at 0.1 C rate, making it promising for the application in flexible Li‐ion batteries.     

3D Porous N‐Doped Graphene Frameworks Made of Interconnected Nanocages for Ultrahigh‐Rate and Long‐Life Li–O2 Batteries

The inferior rate capability and poor cycle stability of the present Li–O₂ batteries are still critical obstacles for practice applications. Configuring novel and integrated air electrode materials with unique structure and tunable chemical compositions is one of the efficient strategies to solve these bottleneck problems. Herein, a novel strategy for synthesis of 3D porous N‐doped graphene aerogels (NPGAs) with frameworks constructed by interconnected nanocages with the aid of polystyrene sphere@polydopamine is reported. The interconnected nanocages as the basic building unit of graphene sheets are assembled inside the skeletons of 3D graphene aerogels, leading to the 3D NPGA with well‐developed interconnected channels and the full exposure of electrochemically active sites. Benefiting from such an unique structure, the as‐made NPGA delivers a high specific capacity, an excellent rate capacity of 5978 mA h g^?1 at 3.2 A g^?1, and long cycle stability, especially at a large current density (54 cycles at 1 A g^?1), indicative of boosted rate capability and cycle life as air electrodes for Li–O₂ batteries. More importantly, based on the total mass of C+Li₂O₂, a gravimetric energy density of 2400 W h kg^?1 for the NPGA–O₂//Li cell is delivered at a power density of 1300 W kg^?1.     

A Composite of Carbon‐Wrapped Mo2C Nanoparticle and Carbon Nanotube Formed Directly on Ni Foam as a High‐Performance Binder‐Free Cathode for Li‐O2 Batteries

Cathode design is indispensable for building Li‐O₂ batteries with long cycle life. A composite of carbon‐wrapped Mo₂C nanoparticles and carbon nanotubes is prepared on Ni foam by direct hydrolysis and carbonization of a gel composed of ammonium heptamolybdate tetrahydrate and hydroquinone resin. The Mo₂C nanoparticles with well‐controlled particle size act as a highly active oxygen reduction reactions/oxygen evolution reactions (ORR/OER) catalyst. The carbon coating can prevent the aggregation of the Mo₂C nanoparticles. The even distribution of Mo₂C nanoparticles results in the homogenous formation of discharge products. The skeleton of porous carbon with carbon nanotubes protrudes from the composite, resulting in extra voids when applied as a cathode for Li‐O₂ batteries. The batteries deliver a high discharge capacity of ≈10 400 mAh g^?1 and a low average charge voltage of ≈4.0 V at 200 mA g^?1. With a cutoff capacity of 1000 mAh g^?1, the Li‐O₂ batteries exhibit excellent charge–discharge cycling stability for over 300 cycles. The average potential polarization of discharge/charge gaps is only ≈0.9 V, demonstrating the high ORR and OER activities of these Mo₂C nanoparticles. The excellent cycling stability and low potential polarization provide new insights into the design of highly reversible and efficient cathode materials for Li‐O₂ batteries.     

A Soft Lithiophilic Graphene Aerogel for Stable Lithium Metal Anode

The lithium metal anode is one of the most promising anodes for next‐generation high‐energy‐density batteries. However, the severe growth of Li dendrites and large volume expansion leads to rapid capacity decay and shortened lifetime, especially in high current density and high capacity. Herein, a soft 3D Au nanoparticles@graphene hybrid aerogel (Au? GA) as a lithiophilic host for lithium metal anode is proposed. The large surface area and interconnected conductive pathways of the Au? GA significantly decrease the local current density of the electrode, enabling uniform Li deposition. Furthermore, the 3D porous structure effectively accommodates the large volume expansion during Li plating/stripping, and the Li_xAu alloy serves as a solid solution buffer layer to completely eliminate the Li nucleation over‐potential. Symmetric cells can stably cycle at 8 mA cm^?2 for 8 mAh cm^?2 and exhibit ultra‐long cycling: 1800 h at 2 mA cm^?2 for 2 mAh cm^?2, and 1200 h at 4 mA cm^?2 for 4 mAh cm^?2, with low over‐potential. Full cells assemble with a Cu@Au? GA? Li anode and LiFePO₄ cathode, can sustain a high rate of 8 C, and retain a high capacity of 59.6 mAh g^?1 after 1100 cycles at 2 C.     

Highly Stable Cycling of Amorphous Li2CO3‐Coated α‐Fe2O3 Nanocrystallines Prepared via a New Mechanochemical Strategy for Li‐Ion Batteries

In this study, an amorphous Li₂CO₃‐coated nanocrystalline α‐Fe₂O₃ hierarchical structure is synthesized for the first time using a facile one‐step mechanochemical process at room temperature, taking advantage of the concurrence of repeated fracture‐cold welding of material's particles and a gas‐solid redox reaction. The conformal coating and hierarchical structure significantly increase the cycling durability and rate capability. Typically, a 1–3 nm thick amorphous Li₂CO₃ layer is conformally coated on Fe₂O₃ nanocrystallines (≈10 nm in size) that form hierarchically aggregated particles 400–800 nm in size by ball milling α‐Fe₂O₃ with LiH in CO₂. The prepared Li₂CO₃‐coated nanocrystalline α‐Fe₂O₃ exhibits highly stable long‐term cyclability as it delivers a reversible capacity of 975 mAh g^?1 with 99% of retention after 400 cycles at 100 mA g^?1. At a high rate of 3000 mA g^?1, its reversible capacity still remains at 537 mAh g^?1, superior to the uncoated counterpart (311 mAh g^?1). Moreover, amorphous Li₂O and Li₂CO₃ coatings are also similarly produced on Fe₂O₃ and NiO nanocrystallines, respectively, representing the general applicability of this mechanochemical approach.     

Graphene Oxide Gel‐Derived,Free‐Standing,Hierarchically Porous Carbon for High‐Capacity and High‐Rate Rechargeable Li‐O2 Batteries

Lithium‐oxygen (Li‐O₂) batteries are one of the most promising candidates for high‐energy‐density storage systems. However, the low utilization of porous carbon and the inefficient transport of reactants in the cathode limit terribly the practical capacity and, in particular, the rate capability of state‐of‐the‐art Li‐O₂ batteries. Here, free‐standing, hierarchically porous carbon (FHPC) derived from graphene oxide (GO) gel in nickel foam without any additional binder is synthesized by a facile and effective in situ sol‐gel method, wherein the GO not only acts as a special carbon source, but also provides the framework of a 3D gel; more importantly, the proper acidity via its intrinsic COOH groups guarantees the formation of the whole structure. Interestingly, when employed as a cathode for Li‐O₂ batteries, the capacity reaches 11 060 mA h g^?1 at a current density of 0.2 mA cm^?2 (280 mA g^?1); and, unexpectedly, a high capacity of 2020 mA h g^?1 can be obtained even the current density increases ten times, up to 2 mA cm^?2 (2.8 A g^?1), which is the best rate performance for Li‐O₂ batteries reported to date. This excellent performance is attributed to the synergistic effect of the loose packing of the carbon, the hierarchical porous structure, and the high electronic conductivity of the Ni foam.     

Platinum‐Coated Hollow Graphene Nanocages as Cathode Used in Lithium‐Oxygen Batteries

One of the formidable challenges facing aprotic lithium‐oxygen (Li‐O₂) batteries is the high charge overpotential, which induces the formation of byproducts, loss in efficiency, and poor cycling performance. Herein, the synthesis of the ultrasmall Pt‐coated hollow graphene nanocages as cathode in Li‐O₂ batteries is reported. The charge voltage plateau can reduce to 3.2 V at the current density of 100 mA g^?1, even maintain below 3.5 V when the current density increased to 500 mA g^?1. The unique hollow graphene nanocages matrix can not only provide numerous nanoscale tri‐phase regions as active sites for efficient oxygen reduction, but also offer sufficient amount of mesoscale pores for rapid oxygen diffusion. Furthermore, with strong atomic‐level oxygen absorption into its subsurface, ultrasmall Pt catalytically serves as the nucleation site for Li₂O₂ growth. The Li₂O₂ is subsequently induced into a favorable form with small size and amorphous state, decomposed more easily during recharge. Meanwhile, the conductive hollow graphene substrate can enhance the catalytic activity of noble metal Pt catalysts due to the graphene‐metal interfacial interaction. Benefiting from the above synergistic effects between the hollow graphene nanocages and the nanosized Pt catalysts, the ultrasmall Pt‐decorated graphene nanocage cathode exhibits enhanced electrochemical performances.     

A Mixed Lithium‐Ion Conductive Li2S/Li2Se Protection Layer for Stable Lithium Metal Anode

Constructing artificial solid‐electrolyte interphase (SEI) on the surface of Li metal is an effective approach to improve ionic conductivity of surface SEI and buffer Li dendrite growth of Li metal anode. However, constructing of homogenous ideal artificial SEI is still a great challenge. Here, a mixed lithium‐ion conductive Li₂S/Li₂Se (denoted as LSSe) protection layer, fabricated by a facile and inexpensive gas–solid reaction, is employed to construct stable surface SEI with high ionic conductivity. The Li₂S/Li₂Se‐protected Li metal (denoted as LSSe@Li) exhibits a stable dendrite‐free cycling behavior over 900 h with a high lithium stripping/plating capacity of 3 mAh cm^?2 at 1.5 mA cm^?2 in the symmetrical cell. Compared to bare Li anode, full batteries paired with LiFePO₄, sulfur/carbon, and LiNi_0.6Co_0.2Mn_0.2O₂ cathodes all present better battery cycling and rate performance when LSSe@Li anode is used. Moreover, Li₂Se exhibits a lower lithium‐ion migration energy barrier in comparison with Li₂S which is proved by density functional theory calculation.     

Improved Performance in FeF2 Conversion Cathodes through Use of a Conductive 3D Scaffold and Al2O3 ALD Coating

FeF₂ is considered a promising conversion compound for the positive electrode in lithium‐ion batteries due to its high thermodynamic reduction potential (2.66 V vs Li/Li⁺) and high theoretical specific capacity (571 mA h g^?1). However, the sluggish reaction kinetics and rapid capacity decay caused by side reactions during cycling limit its practical application. Here, the fabrication of Ni‐supported 3D Al₂O₃‐coated FeF₂ electrodes is presented, and it is shown that these structured electrodes significantly overcome these limitations. The electrodes are prepared by iron electrodeposition on a Ni support, followed by a facile fluorination process and Al₂O₃ coating by atomic layer deposition. The 3D FeF₂ electrode delivers an initial discharge capacity of 380 mA h g^?1 at a current density of 200 mA g^?1 at room temperature. The 3D scaffold improves the reaction kinetics and enables a high specific capacity by providing an efficient electron pathway to the insulating FeF₂ and short Li diffusion lengths. The Al₂O₃ coating significantly improves the cycle life, probably by preventing side reactions through limiting direct electrode–electrolyte contact. The fabrication method presented here can also be applied for synthesis of other metal fluoride materials on different 3D conductive templates.     

2D Nanospace Confined Synthesis of Pseudocapacitance‐Dominated MoS2‐in‐Ti3C2 Superstructure for Ultrafast and Stable Li/Na‐Ion Batteries

Exploring a universal strategy to implement the precise control of 2D nanomaterials in size and layer number is a big challenge for achieving ultrafast and stable Li/Na‐ion batteries. Herein, the confined synthesis of 1–3 layered MoS₂ nanocrystals into 2D Ti₃C₂ interlayer nanospace with the help of electrostatic attraction and subsequent cetyltrimethyl ammonium bromide (CTAB) directed growth is reported. The MoS₂ nanocrystals are tightly anchored into the interlayer by 2D confinement effect and strong Mo? C covalent bond. Impressively, the disappearance of Li⁺ intercalated into MoS₂ reduction peak is successfully observed for the first time in the experiment, showing in a typical surface‐controlled charge storage behavior. The pseudocapacitance‐dominated contribution guarantees a much faster and more stable Li/Na storage performance. As predicted, this electrode exhibits a very high Li⁺ storage capacity of 340 mAh g^?1 even at 20 A g^?1 and a long cycle life (>1000 times). It also shows an excellent Na⁺ storage capacity of 310 mAh g^?1 at 1 A g^?1 with a 1600 times high‐rate cycling. Such impressive confined synthesis strategy can be extended to the precise control of other 2D nanomaterials.     

Layered P2‐Type K0.65Fe0.5Mn0.5O2 Microspheres as Superior Cathode for High‐Energy Potassium‐Ion Batteries

Potassium‐ion batteries have been regarded as the potential alternatives to lithium‐ion batteries (LIBs) due to the low cost, earth abundance, and low potential of K (?2.936 vs standard hydrogen electrode (SHE)). However, the lack of low‐cost cathodes with high energy density and long cycle life always limits its application. In this work, high‐energy layered P2‐type hierarchical K_0.65Fe_0.5Mn_0.5O₂ (P2‐KFMO) microspheres, assembled by the primary nanoparticles, are fabricated via a modified solvent‐thermal method. Benefiting from the unique microspheres with primary nanoparticles, the K⁺ intercalation/deintercalation kinetics of P2‐KFMO is greatly enhanced with a stabilized cathodic electrolyte interphase on the cathode. The P2‐KFMO microsphere presents a highly reversible potassium storage capacity of 151 mAh g^?1 at 20 mA g^?1, fast rate capability of 103 mAh g^?1 at 100 mA g^?1, and long cycling stability with 78% capacity retention after 350 cycles. A full cell with P2‐KFMO microspheres as cathode and hard carbon as anode is constructed, which exhibits long‐term cycling stability (>80% of retention after 100 cycles). The present high‐performance P2‐KFMO microsphere cathode synthesized using earth‐abundant elements provides a new cost‐effective alternative to LIBs for large‐scale energy storage.     

Solid‐State Plastic Crystal Electrolytes: Effective Protection Interlayers for Sulfide‐Based All‐Solid‐State Lithium Metal Batteries

All‐solid‐state lithium metal batteries (ASSLMBs) have attracted significant attention due to their superior safety and high energy density. However, little success has been made in adopting Li metal anodes in sulfide electrolyte (SE)‐based ASSLMBs. The main challenges are the remarkable interfacial reactions and Li dendrite formation between Li metal and SEs. In this work, a solid‐state plastic crystal electrolyte (PCE) is engineered as an interlayer in SE‐based ASSLMBs. It is demonstrated that the PCE interlayer can prevent the interfacial reactions and lithium dendrite formation between SEs and Li metal. As a result, ASSLMBs with LiFePO₄ exhibit a high initial capacity of 148 mAh g^?1 at 0.1 C and 131 mAh g^?1 at 0.5 C (1 C = 170 mA g^?1), which remains at 122 mAh g^?1 after 120 cycles at 0.5 C. All‐solid‐state Li‐S batteries based on the polyacrylonitrile‐sulfur composite are also demonstrated, showing an initial capacity of 1682 mAh g^?1. The second discharge capacity of 890 mAh g^?1 keeps at 775 mAh g^?1 after 100 cycles. This work provides a new avenue to address the interfacial challenges between Li metal and SEs, enabling the successful adoption of Li metal in SE‐based ASSLMBs with high energy density.     

Mesoporous Carbon Nanocube Architecture for High‐Performance Lithium–Oxygen Batteries

One of the major challenges to develop high‐performance lithium–oxygen (Li–O₂) battery is to find effective cathode catalysts and design porous architecture for the promotion of both oxygen reduction reactions and oxygen evolution reactions. Herein, the synthesis of mesoporous carbon nanocubes as a new cathode nanoarchitecture for Li–O₂ batteries is reported. The oxygen electrodes made of mesoporous carbon nanocubes contain numerously hierarchical mesopores and macropores, which can facilitate oxygen diffusion and electrolyte impregnation throughout the electrode, and provide sufficient spaces to accommodate insoluble discharge products. When they are applied as cathode catalysts, the Li–O₂ cells deliver discharge capacities of 26 100 mA h g^?1 at 200 mA g^?1, which is much higher than that of commercial carbon black catalysts. Furthermore, the mesoporous nanocube architecture can also serve as a conductive host structure for other highly efficient catalysts. For instance, the Ru functionalized mesoporous carbon nanocubes show excellent catalytic activities toward oxygen evolution reactions. Li–O₂ batteries with Ru functionalized mesoporous carbon nanocube catalysts demonstrate a high charge/discharge electrical energy efficiency of 86.2% at 200 mA g^?1 under voltage limitation and a good cycling performance up to 120 cycles at 400 mA g^?1 with the curtaining capacity of 1000 mA h g^?1.     

A Moisture‐ and Oxygen‐Impermeable Separator for Aprotic Li‐O2 Batteries

Despite the unparalleled theoretical gravimetric energy, Li‐O₂ batteries are still under a research stage because of their insufficient cycle lives. While the reversibility in air‐cathodes has been lately improved significantly by the deepened understanding on the electrode–electrolyte reaction and the integration of diverse catalysts, the stability of the Li metal interface has received relatively much less attention. The destabilization of the Li metal interface by crossover of water and oxygen from the air‐cathode side can indeed cause as fatal degradation for the cycle life as the irreversibility of the air‐cathodes. Here, it is reported that cheap poreless polyurethane separator can effectively suppress this crossover while allowing Li ions to diffuse through selectively. The polyurethane separator also protects Li metal anodes from redox mediators used for enhancing the reversibility of the air‐cathode reaction. Based on the Li metal protection, a persistent capacity of 600 mAh g^?1 is preserved for more than 200 cycles. The current approach can be readily applicable to many other rechargeable batteries that suffer from similar interfacial degradation by side products from the other electrode.     

Cobalt‐Doped SnS2 with Dual Active Centers of Synergistic Absorption‐Catalysis Effect for High‐S Loading Li‐S Batteries

The application of Li‐S batteries is hindered by low sulfur utilization and rapid capacity decay originating from slow electrochemical kinetics of polysulfide transformation to Li₂S at the second discharge plateau around 2.1 V and harsh shuttling effects for high‐S‐loading cathodes. Herein, a cobalt‐doped SnS₂ anchored on N‐doped carbon nanotube (NCNT@Co‐SnS₂) substrate is rationally designed as both a polysulfide shield to mitigate the shuttling effects and an electrocatalyst to improve the interconversion kinetics from polysulfides to Li₂S. As a result, high‐S‐loading cathodes are demonstrated to achieve good cycling stability with high sulfur utilization. It is shown that Co‐doping plays an important role in realizing high initial capacity and good capacity retention for Li‐S batteries. The S/NCNT@Co‐SnS₂ cell (3 mg cm^?2 sulfur loading) delivers a high initial specific capacity of 1337.1 mA h g^?1 (excluding the Co‐SnS₂ capacity contribution) and 1004.3 mA h g^?1 after 100 cycles at a current density of 1.3 mA cm^?2, while the counterpart cell (S/NCNT@SnS₂) only shows an initial capacity of 1074.7 and 843 mA h g^?1 at the 100th cycle. The synergy effect of polysulfide confinement and catalyzed polysulfide conversion provides an effective strategy in improving the electrochemical performance for high‐sulfur‐loading Li‐S batteries.     

Few‐Layered SnS2 on Few‐Layered Reduced Graphene Oxide as Na‐Ion Battery Anode with Ultralong Cycle Life and Superior Rate Capability

Na‐ion Batteries have been considered as promising alternatives to Li‐ion batteries due to the natural abundance of sodium resources. Searching for high‐performance anode materials currently becomes a hot topic and also a great challenge for developing Na‐ion batteries. In this work, a novel hybrid anode is synthesized consisting of ultrafine, few‐layered SnS₂ anchored on few‐layered reduced graphene oxide (rGO) by a facile solvothermal route. The SnS₂/rGO hybrid exhibits a high capacity, ultralong cycle life, and superior rate capability. The hybrid can deliver a high charge capacity of 649 mAh g^?1 at 100 mA g^?1. At 800 mA g^?1 (1.8 C), it can yield an initial charge capacity of 469 mAh g^?1, which can be maintained at 89% and 61%, respectively, after 400 and 1000 cycles. The hybrid can also sustain a current density up to 12.8 A g^?1 (≈28 C) where the charge process can be completed in only 1.3 min while still delivering a charge capacity of 337 mAh g^?1. The fast and stable Na‐storage ability of SnS₂/rGO makes it a promising anode for Na‐ion batteries.     

Lithium Titanate Anode Thin Films for Li‐Ion Solid State Battery Based on Garnets

Solid state electrolytes, such as Li‐Garnets, are fastest Li‐ionic conductor materials that have attracted attention for safe hybrid and full solid state battery architectures. Turning to oxide‐based low voltage anodes gives opportunities to avoid Li‐dendrite formation and also to reach full thin film microbattery architectures based on garnets as high energy density replacement for supercapacitors. Herein, it is demonstrated that Li₄Ti₅O₁₂ thin films deposited by pulsed laser deposition can show stable structures and cycling kinetics reaching almost close to theoretical capacity of 175 mAh g^?1 when combined to Li_6.25Al_0.25La₃Zr₂O₁₂ pellets. Stable operation at room temperature with 90% of theoretical capacity retention at 2.5 mA g^?1 over 22 cycles is achieved on bilayer half cell batteries. Rate capability studies show promising charge and discharge capacities and act as a case study for the well‐known Li₄Ti₅O₁₂ thin film anode, demonstrating its good compatibility with the investigated solid garnet electrolyte. This gives new perspective on the use of oxide‐based low voltage anodes for future strategies avoiding Li‐dendrite formation or safe solid state microbattery thin film assemblies based on Li‐garnets.     

Quasi‐Stable Electroless Ni–P Deposition: A Pivotal Strategy to Create Flexible Li–S Pouch Batteries with Bench Mark Cycle Stability and Specific Capacity

Development of flexible Li–S batteries brings along the flourishing prospective for energy‐hungry wearable devices. However, it is still seriously restricted due to lack of facile methods to solve its inherent problems and flexible device‐related current collection issues. Herein, quasi‐stable electroless deposition method is firstly proposed to solve these problems by fabricating 3D tunable Ni–P networks in the C/S free‐standing electrode. The ultrathin Ni–P layers which are highly conductive and strongly adhesive with electrode substrates improve the electronic conductivity by two orders of magnitude and rise initial specific capacity from 1200 to 1600 mAh g^?1. The harmful shuttle effect of polysulfide is also effectively alleviated due to the chemical adsorption and physical sieving properties of the 3D networks. The flexible pouch Li–S batteries assembled with commercially applicable structure also show high flexibility and as high as 1420 mAh g^?1 output capacity at 0.1C in cycling test. This method can definitely be extended to other flexible devices such as Li‐ion batteries, Li–O₂ batteries, and supercapacitors.     

Hierarchical Co3O4 Nanofiber–Carbon Sheet Skeleton with Superior Na/Li‐Philic Property Enabling Highly Stable Alkali Metal Batteries

Uncontrollable dendritic behavior and infinite volume expansion in alkali metal anode results in the severe safety hazards and short lifespan for high‐energy batteries. Constructing a stable host with superior Na/Li‐philic properties is a prerequisite for commercialization. Here, it is demonstrated that the small Gibbs free energy change in the reaction between metal oxide (Co₃O₄, SnO₂, and CuO) and alkali metal is key for metal infusion. The as‐prepared hierarchical Co₃O₄ nanofiber–carbon sheet (CS) skeleton shows improved wettability toward molten Li/Na. The 3D carbon sheet serves as a primary framework, offering adequate lithium nucleation sites and sufficient electrolyte/electrode contact for fast charge transfer. The secondary framework of Co/Li₂O nanofibers provides physical confinement of deposited Li and further redistributes the Li⁺ flux on each carbon fiber, which is verified by COMSOL Multiphysics simulations. Due to the uniform deposition behavior and near‐zero volume change, modified symmetrical Li/Li cells can operate under an ultrahigh current density of 20 mA cm^?2 for more than 120 cycles. When paired with LiFePO₄ cathodes, the Li/Co–CS cell shows low polarization and 88.4% capacity retention after 200 cycles under 2 C. Convincing improvement can also be observed in Na/Co–CS symmetrical cells applying NaClO₄‐based electrolyte. These results illustrate a significant improvement in developing safe and stable alkali metal batteries.